1. Field of the Invention
The present invention relates to a solar cell, and more particularly, to a dye-sensitized solar cell having an electrode formed of a new material, so that the dye-sensitized solar cell has improved flexibility, processability, and efficiency.
The present invention is derived from a research project supported by the Information Technology (IT) Research & Development (R&D) program of the Ministry of Information and Communication (MIC) [2009-S-006-02, Component Module for Ubiquitous Terminal].
2. Description of the Related Art
A dye-sensitized solar cell is a new type of a low-cost solar cell that was developed in Switzerland in 1991 by a research team lead by Michael Gratzel of the Ecole Polytechnique Federale de Lausanne (EPFL). A dye-sensitized solar cell is based on a photoelectrochemical system including photosensitive dye molecules which can generate electrons by absorbing visible light, and a transition metal semiconductor oxide and an electrolyte which transfer the generated electrons to an electrode.
FIG. 1 is a schematic view of a dye-sensitized solar cell for explaining the operational principle of the dye-sensitized solar cell. Referring to FIG. 1, sunlight is incident through an anode 10 on dye molecules 22 which are present on a surface of titanium oxide (TiO2) 21, which is a transition metal semiconductor oxide. Because the dye molecules 22 are very small, TiO2 is used as a scaffold to retain a number of dye molecules in a 3-D medium with respect to a surface area of a given electric cell. A photon that reached the dye molecule 22 with sufficient energy to be absorbed excites the dye molecule 22 to an excited state, and thus the dye molecule 22 emits an electron (e−). The electron (e−) emitted from the dye molecule 22 is immediately injected into a conduction band of TiO2 21 and is moved to the anode 10 by a chemical diffusion gradient. Meanwhile, the dye molecule 22, which has lost one electron, oxidizes iodine ion (I−) in an electrolyte 23 into a 3-iodine ion (I3−), thereby obtaining an electron. The 3-iodine ion (I3−) is diffused mechanically to a counter electrode 30 and regains there an electron, i.e., a counter electron coming through an external circuit.
The dye-sensitized solar cell is manufactured using a low-cost material via a simple manufacturing process, compared to a conventional silicon solar cell. Also, since the efficiency of the dye-sensitized solar cell is not much less than that of the silicon solar cell, many research studies have been performed to further develop dye-sensitized solar cells.
Meanwhile, as the application fields of solar cells have considerably expanded, flexible solar cells are in high demand. However, a conventional dye-sensitized solar cell includes an anode formed of a glass substrate, on a surface of which a conductive layer is formed, and when a nano-particle semiconductor oxide is attached/sintered thereon, the flexibility of glass is decreased, and thus, a bendable dye-sensitized solar cell cannot be realized. Thus, manufacturing and utilizing dye-sensitized solar cells have been difficult.
In order to address this problem, a thin metal substrate has been used as an electrode instead of the conductive glass substrate, as disclosed in Korean Patent Laid-Open Gazette No. 10-2005-0116869. However, according to this patent application, when the metal substrate is thin, the dye-sensitized solar cell is sufficiently flexible but the intensity thereof is decreased; and when the metal substrate is thick, the flexibility of the dye-sensitized solar cell is not great. Also, due to the low light transmittivity of a metal, an anode including a nano-particle semiconductor oxide should always be placed far away from a light source.